what is chromosomes in science

A chromosome is a thread-like structure made up of DNA and proteins called histones. Chromosomes are found in the nucleus of each cell and carry genetic information. Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections or "arms". The location of the centromere on each chromosome gives the chromosome its characteristic shape and can be used to help describe the location of specific genes. Chromosomes are not visible in the cells nucleus, even under a microscope, when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division. Humans have 23 pairs of chromosomes, with 22 pairs being autosomes and one pair being sex chromosomes. Chromosomes vary in number and shape among living organisms. Chromosomes are essential to the cell division that makes our lives possible, as they allow DNA to be accurately copied during cell division.